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    <title>Document</title>
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    <script>
        // 五种基本数据类型
        let num = 1;
        let str = '字符串';
        let bool = true;
        let und = undefined;
        let nul = null;

        console.log(typeof num);  // 字符串
        console.log(typeof str);
        console.log(typeof bool);
        console.log(typeof und);
        console.log(typeof nul);  // object

        // 引用数据类型  object function Symbol BigInt
        let obj = {};
        let fn = function () { };
        let arr = [];


        // 原始数据类型！！
        let sy1 = Symbol('abc');// 生成一个唯一的字符串，uuid 
        let sy2 = Symbol('abc');// 生成一个唯一的字符串，uuid 
        let big1 = 300000000n; // 超越原有js中可处理的最大数值，处理大额数值
        let big2 = BigInt(300000000); // 超越原有js中可处理的最大数值，处理大额数值
        console.log(typeof arr, 'arr:'); // object
        console.log(typeof obj)
        console.log(typeof fn)
        console.log(typeof sy)
        console.log(typeof big1);


        let sum = big1 + big2;
        console.log(sum == 600000000)
        console.log(sum === 600000000)
        console.log(sy1, sy2, sy2 === sy1)



    </script>
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